The present invention relates in general to providing electrical power for volatile memories in electrical equipment used in transportation vehicles, and more specifically to a backup rechargeable battery for providing power to volatile memories during failure of a primary power source.
Many types of electrical equipment in automobiles, such as an engine control computer, an audio system, and a clock, take advantage of volatile electronic (semiconductor) memory for storing information used by the equipment. A volatile memory retains information only as long as energizing power is applied, but has advantages of low cost, small size, and the ability to have the memory contents rewritten numerous times. Non-volatile, rewriteable memory that maintains its memory contents without continuous application of power is available and is often used for critical information storage, but suffers from the disadvantages of greater expense and larger size. Thus, to minimize cost, noncritical information is typically kept in volatile memory in many types of electrical equipment. For example, a automotive audio system typically employs volatile memory for storing radio station resets, last volume setting, last station tuned, and other radio and audio control information in volatile memories. Automotive clocks having digital displays typically use volatile memory exclusively whether the clock is contained as part of the audio system or is a separate unit contained on a vehicle dashboard. An electronic engine control (EEC) computer employs volatile memory for various adaptive engine parameters for optimizing performance such as idle airflow.
In prior art automotive electrical systems, the electrical equipment including the volatile memories receives electrical power from a main vehicle battery. A failure of the vehicle battery due to its discharge or removal results in the loss of information from volatile memories powered by the vehicle battery. Therefore, each occurrence of a dead battery or replacement of a battery necessitates reprogramming of volatile memories to restore the lost information. For example, an automobile user must manually reset a clock and manually re-enter the desired radio station presets after failure of the main battery. With regard to lost memory contents in the EEC, engine operation can be established using base values with subsequent redetermination of lost parameter values; however, engine performance and emissions may suffer during the interim time period.
A further problem resulting from main battery failure is the inability to operate even low power electrical appliances in the vehicle. For example, illumination by a courtesy dome light is unavailable while the battery is dead.